Disposal of sludge from residential or industrial sewage facilities is often accomplished by burning or gasification.
For this purpose the sludge is thermally dried, ground or crushed if necessary, and fed into the disposal reactor (combustion furnace, gasification reactor) as dried dust.
It is also possible to feed the sludge to the disposal reactor as an aqueous suspension by means of a pump. In this case, the suspension is finely dispersed within the disposal reactor by means of known nozzle constructions and is then burned or gasified.
It appears that much sludge, particularly sludge from sewage facilities with microbiological purification stages, takes on the consistency of a thick mush or pulp even at a relatively low solids content of 15% or less and can no longer be pumped with conventional pumps and also evades sufficient atomization within the disposal reactor. As a result of feeding sludge with a correspondingly low concentration of solids, the disposal process is burdened with large quantities of water which must at least be evaporated within the disposal reactor. This causes additional energy costs and hampers economic efficiency. However, a preliminary thermal drying of the sludge also involves heavy costs.
Thick-matter pumps have been introduced which can pump pasty and plastic materials. Such thick-matter pumps are also used to convey sludge from which water has been removed mechanically, e.g. by means of centrifuges or filter presses, until reaching a dry-matter content of 30 to 35%, the sludge being in a more or less plastic form as a filter cake. In this type of conveying, which as a rule involves high pressure losses per meter length of pipe, the material leaves the conveying pipeline as a closed, cohesive string. For this reason, atomization within a disposal reactor can be achieved by conventional means only at a high cost if at all, so that the advantage of a drastic reduction in the loading of the disposal reactor with water cannot be exploited.